Polyester bottles, for carbonated beverages, having petaloid bases to provide a self-standing ability with a one piece construction are known in the prior art and are commercially available. Such prior art bottles have been constructed of biaxially oriented PET by the known process of blow molding. These prior art one piece bottle constructions have permitted the commercially viable mass production of self-standing beverage containers without the use of a separate base molding utilized in earlier constructions in which the base of the bottle was hemispherical and rendered self-standing by the addition of a separate base unit attached to the hemispherical base by an adhesive. Such two piece constructions do not lend themselves to recycling and were relatively expensive in terms of material and production costs.
Production costs and, more particularly, material costs has led in recent years to substantial research and development in attempts to produce a commercially viable self-standing one piece bottle, for carbonated beverages, which can be produced economically and which performs reliably both in terms of storage and transportation as well as the ability to provide reliable and stable self-standing performance in use.
While this prior art research and development has led to commercially viable products, the viability of these products has been achieved at the expense of the incorporation of additional material to provide the required bottle integrity and stability for commercial use. This additional material was necessitated by the need to design the base of a one-piece bottle which provides a self-standing ability with the consequent elimination of the simple, lightest and most strength effective prior art base form, namely the hemisphere.
Prior art designs, utilizing a hemispherical base, constructed of biaxially oriented PET, such as are found in the commercial market, typically weigh between 46 and 48 grams in the 2 liter size (to this must be added 13 to 16 grams of polyethylene or other plastic material in the separate base which is attached to the hemispherical base to provide standing stability). By comparison, present day commercially available self-standing petaloid base biaxially oriented PET 2 liter bottles weigh from 50 to 56 grams with an average weight of approximately 53.5 grams.
Based on a conservative estimate of 5 billion bottles produced per year and a PET price of $(US)0.7 per pound, a 1 gram increase in the PET content of a bottle will cost approximately $(US)7.7 million per year. Consequently, although the separate polyethylene base is eliminated, the achievement of one-piece self-standing 2 liter PET bottles, meeting the necessary integrity and stability requirements of the industry, as they are currently available has resulted in an increased PET material cost, on the basis of 5 billion bottles per year, of approximately $(US)50 million.
It is an object of the present invention to provide a self-standing petaloid base biaxially oriented polyester bottle for carbonated beverages which is significantly lighter in weight than existing commercially available petaloid base bottle designs without any significant increase in production costs and while meeting industry requirements with respect to integrity and stability during storage, transportation and use.
It is also an object of the present invention to provide improved stress crack resistance of the base.